In the field of civil engineering works that excavates earth, stone and so on, construction machines such as a hydraulic excavator (excavator) have been used in works.
This type of hydraulic excavator mainly includes a lower traveling unit, a revolving unit that is revolvably mounted to the lower traveling unit, and an operator compartment (cab) that is fixedly arranged on the revolving unit and accommodates an operator.
Recent years, operator rollover protection structure for operator compartments compliant with requirements such as EPOS (Excavator's Operator protection structure for over 6 tons hydraulic excavators: Japan Construction Mechanization Association Standard) is especially getting important. The rigidity improvement of cab structure becomes an important issue in terms of safety.
For example, Japanese Patent Laid-Open Publication TOKUKAI No. HEI 9-25648 (published on Jan. 28, 1997) discloses a cab structure for a construction machine (working vehicle) that includes a support pole that is composed of combined inner and outer plates, and a reinforcing member such as a steel pipe that is arranged in hollow space inside the support pole.
According to this structure, the rigidity of the cab structure can be greatly improved against deformation in case of a rollover accident of the construction machine as compared with a cab structure that is composed of only sheet metal members such as inner and outer plates.